I used a passenger seat of a t5 , ended up making a few frames under the van out of 6mm angle steel bolted through the chassis (behind drivers seat take exhaust and Heatshield off its pretty open )
I then bolted up from below through the seat so I can take it out leaving the bolts in place
I used a 6mm 80x80 angle under the rear of the seat and bolted an additional seatbelt to that and ran it under the seat cover alongside the origional on
All in all everything is bolted down solidly and the seat folds as it should with 2 working belts and no additional floor heigh so it's possible just headscratchy