A fold down would be ideal, but it would then need to convert to a double for when the bikes not there, I have gone google t5 conversion mad over the last week.
This is how I slept in the van for a week on my drive back from Ibiza, I am not saying I was unprepared, but it was lucky I had my work jacket to wear over my legs at night.(legs through the arm holes)
Awning/underbody lights, fridge, kettle, phones, internal lights. I'd stick a leisure battery(or two depending on space) in, could charge it by solar (or alternator? - Phil?). Then wire a few sockets on a 2.5 radial back to a 16 plug. One 16a coupler from the hook up, and another coupler would be the 240v feed from the inverter, so you can switch between hook up and battery. The hook up needs to be on a 13A FCU or a 16A breaker in a small consumer unit. The fridge should be fed on a fused line from the leisure battery. You could stick the hook up under the body too. There's a bit of space under rear bumper IIRC. Stick a USB socket in the back off the van battery too.
******* hell, hope you clear it out before converting it... Still a lot of space in the SWB if you plan well. Pull off the original plylining and fill it with rockwool, then board over.
I was thinking solar to just top up the battery, I was going to put the leisure batt under the bonnet, most t5 owners put theirs under the passenger seat but I want to be able to remove it if need be, I would get the 240 hook up under there too.
I worked for a while in a super yacht boatyard, we used to use a polyisocyanurate core plywood. It was strong and light.
I like it, but I need to get my motorbike in on the off side. I was thinking something like that on the near side, that would house a kitchen type set up (kettle, burner, fridge unit etc) also removable, so cooking can happen outside the van, but also leaving enough room for a pull out slide out bed thingy. I don't want much out of it. I can see this project going the same way as my "Ultra Bench" I have been researching these vw campers for months now and they go for silly silly money, (vw scene tax) an 08 converted van £25k, its money for old rope and a piece of urine to do if you have some skills, possible future business, mmmm
Use LED 12v lighting, there some nice low profile interior strip lights around, & spots from makers like LED Autolamps & easier on the battery. And no heat.