I have a '93 Casita
16' that did not come with a tank rack.
You can see from the picture where there is a rusty circle, it looks like the PO had a single bottle sitting there at one point.
There is a hole in the cross-bar in the center like you would use for one of the threaded-rod hold downs for a dual tank setup.
There are also four holes on the beams that run from side to side, 2 of them have bolts in them, and 2 of them are empty.
I do not see us using a lot of propane
and would like to just mount one bottle.
The only thing I have been able to turn up from searching the internet is a J style rack for singles, but it is for mounting on a vertical surface, like on a wall.