We have the Propex HS2000 and it is sorta marginal for output with our 24" high top. If you have a penthouse and do cold weather I would recommend the HS2800.
The best propane tank and access door I found was from Sportsmobile. They have two sizes - both 10" diameter with one longer than the other. There isn't as much room under the van on the passenger side due to the step for the side door. The 10" diameter tank would hang down quite a ways on the passenger side. There are 6" diameter tanks available (used for Westy's) that would fit better there, but they are smaller.
For the 10" tanks mounted on the driver side, since the tank is mounted higher the valves need to be lower. The SMB tank has the mounting brackets on the ends, which will make it easier to mount than the top brackets.
The SMB access door works very well:
Although it needs to be painted to match
OBTW we got the 8 gallon propane tank and it will run our furnace and frig for less than a week in cold weather. In the summer it will run the frig alone for over a week.