Not the prettiest install, being honest, but who cares what a money-making machine looks like
I like the exhaust through the floor. Couldn't do that on mine, apparently Transits have a sodding great metal beam that runs underneath just there, you can't fit an exhaust through the floor on them. Thankfully I don't do many jobs like terraced streets where people walk right past the machine, but when I do I'm a bit concerned about the exhaust blowing straight out the side.
I'm a bit concerned about the layout actually. Upright water tank right up against the bulkhead, surely there's a risk over being overweight on the front axle? That's almost a third of a tonne of water sitting there. Also being just behind the front seats is a bit of a worry in a high-speed crash. It looks like the bulkhead is metal though? If so that's a lot safer than just a bit of plywood to protect you!
I must admit there is an advantage of an upright fresh tank - it doesn't matter so much if you're parked on a slope, you'll always be able to run your tank at fairly low levels. With my submount tank if I'm parked facing downhill on a decent slope I can have 100L of water in there and it doesn't come up the the outlet which is right at the back end of the tank!
Is the floor of the van waterproofed? Too late now really if it isn't, you'll never be able to do it properly with the machine in there.
Did you insulate behind the plywood before the machine was installed?
When the frosts set in you're going to be literally burning money trying to heat an un-insulated van. I'd highly recommend continuing the ply up the sides and all the way across the roof, with loft insulation behind it. Do all the doors as well, use ]9mm on the back doors so you can screw stuff to it. Also give the ply a coat of paint to waterproof it. Will make it look all nice and neat too
You're going to have to think about use of space in the back. Everything is bolted to the floor, taking up a lot of room, so you're going to have to get a bit creative. Have you got racking along the nearside wall, out of shot in the photos?
One thing you could do to use space better is build a box over one of the wheel arches and sit the hose reel on top. You could then use the box as a a little cubby-hole.
Those packs of different storage hooks you get from DIY shops are very useful, mounting your wands on hooks on the roof is a very good way of storing them.
Sorry for the long-winded rambling post!