[lxntxn]

Ah. If the nuts are welded to the plate, then yes... doesn't look like they are. 👍

I have purchased them from Yogi's on that ebay listing, and can assure you that they are indeed welded to the plate. Look at the left image. Or search for other "Seatbelt anchor kit" or "seat belt anchor plate" and you will see other options and more images

 

[Lugnut]

I was able to sneak bolts and 3/16 stainless steel plates just over and past the rounded edge of the gas tank. They make a wire/spring gizmo specifically for threading them into tight spaces. They often come with the tow hitches purchased from ETrailer. Amazon has them too.

 

[photony]

One of the things I try to keep in focus when building the van/RV is that everything can/should be removable.

So... I'm really close to mounting the second-row seat in our 2023 van and I'm weighing my options in light of this issue. The real challenge / issue is that I need to remove the fuel tank to bolt it in. And I'll have to remove the water tank in the future, as well. This is an issue because it would be easy enough to really solidly bolt the seat-base in with both of those out... but then impossible to dismount / remove it without removing those two tanks in the future.

I have considered L-Track (already purchased) for this as well... but then I still have the floor through-bolted and can't be removed without removing both tanks.

The IDEAL setup would be welded nuts on the bottom of the van - just like stock Passenger seat mounts. But I'm not crazy about welding them on there... and killing all the paint and resulting in future rust.

Another possible is using VHB to tape plates and nuts down there... they'd just need to stay in place when the seat is removed. But then I'd need some way to get a wrench on them when loosening / tightening... so I'm right back where I started.

Right now, I'm leaning toward L-Track - and getting non-flanged so the floor can be removed while leaving the L-Track bolted in place.

Any other options or designs anyone can think of?

How about a plate that's wide enough to span to easily accessible bolt locations? Then mount the base to that. I had a seat mount in one of my vans that had a plate I mounted as a 3rd seat in one van. Threw a latch , and the seat came out. Don't forget seatbelt points too. Maybe adapt a seat from a minivan.

 

[dalklein]

Good idea to have a look at how anything significant like seats, belts or tie down points all have some reinforcement underneath.

I used a transit seat in my promaster. (Researching and shopping for the bench seat were my reason for joining the transit forum)

I wanted a raised position to match the front seats. I made a pair of sturdy risers duplicating the rail mount geometry. I made reinforcement angle plates with nuts welded to them, under the van. The angle plates are bolted and sikaflex 221'd to the sides of the unibody cross beams or longitudinal main structure.
No welding on the van, except initial tack weld of the large nuts to the reinforcement plates, once everything lined up. Then took out, welded the nuts more securely, cleaned up and painted, etc. Then reassembled with adhesive. I wouldn't weld to the van for this type of thing, the metal is pretty thin.

https://photos.app.goo.gl/tE3uow7uLCr68eHA7

 

[gregoryx]

How about a plate that's wide enough to span to easily accessible bolt locations? Then mount the base to that. I had a seat mount in one of my vans that had a plate I mounted as a 3rd seat in one van. Threw a latch , and the seat came out. Don't forget seatbelt points too. Maybe adapt a seat from a minivan.

Wouldn't that be nice? No chance of a single plate. There's beams segregating where just the four main bolts would go... but once it's bolted, it's good. The Broad Arrow seats include the seatbelts.

...
I used a transit seat in my promaster. (Researching and shopping for the bench seat were my reason for joining the transit forum)
...

Thx for the input. Nice work getting it to work there!

 

[VanBot]

Note that ISO Class 10.9 and Grade 8 hardware will loose its temper when welded. The result will be the strength of mild steel. When torquing 10.9 or 8 bolts into those de-tempered nuts, they will strip or yield. Don't weld them!

Instead, place a second, thinner steel plate over the structural plate. Cut hex bolt patterns in the second plate that align with the nuts and bolt pattern. Use flange nuts. Then sandwich the nuts between the structural plate and the secondary plate to capture the nuts. Screw or glue the two plates together.

 

[gregoryx]

Note that ISO Class 10.9 and Grade 8 hardware will loose its temper when welded. The result will be the strength of mild steel. When torquing 10.9 or 8 bolts into those de-tempered nuts, they will strip or yield. Don't weld them!

Instead, place a second, thinner steel plate over the structural plate. Cut hex bolt patterns in the second plate that align with the nuts and bolt pattern. Use flange nuts. Then sandwich the nuts between the structural plate and the secondary plate to capture the nuts. Screw or glue the two plates together.

FWIW, I ended up NOT welding the weld-nuts. I used captured floating nuts and they're mounted to Rivnuts (nothing to do with the structure / strength - just to hold them in place), keeping the captured nut un-affected by heat or anything else.

One example: 1/2" bar is just to level the mount between rib/valley; bar and disc have holes drilled through them for the mount bolts; those bolts go into rivnuts in the sheet-metal; 12.9 bolts come through from the L-Track on the top into these captured nuts. In my mind, this seems pretty solid - with energy spread through that round plate (that came with the seat-base we purchased). Hopefully, we'll never find out if it's not solid. 🤞

 

[GROOVY2]

Look at Cleco - used in airplane construction - come in several diameters -
very Strong - easy install / remove -