I mounted mine under the bus. Couldn't see any reason to get to it from inside the bus, tank's on all the time, since I use gas for cooking.
I just made a 3 sided box (with a bottom) and bolted it to the side rib and the angle iron at the bottom of the skirt and a piece of allthread at the front through the floor joist for a little more support.
It's just as wide as the tank so it doesn't rock fore and aft and just a little deeper and a little taller to allow some room to tip it in.
Screwed a Harbor Freight cargo strap to the back wall, used a large fender washer so it wouldn't pull through and there's
a 1x2 cleat in the front at the bottom to keep it from slippin' out like a short kid under a seat belt.
I didn't see the need for some great metal cabinet with welding and bolting and stuff - most travel trailers have these things sittin' right out on the tongue so a great tank protection scheme isn't really neccessary, just needed something that would make sure the bus and the tank were in the same place when you stop. With no front there's plenty of ventilation.
In the summer I use one hose - just to the stove -the hose goes up through a hole in the floor. The tank's right under the kitchen - and the hole filled with that expanding foam stuff.
In the winter I put a Tee on the tank and run another hose up through the floor with expanding foam stuff for the heater (Mr. Heater). In the summer I take out the heater and the hose and and squirt foam in the hole.
You do have to slide under there to change the tank, but I've not seen that as much of a problem. My last tank change was in March this year (I'm fulltime) and I should have to change it here pretty soon, since I'm going to start needing heat here. During the winter it's a tank a week.