I had the exact same problem
in my 2007 Casita
I solved the problem by removing both the right and left drawer slides with their assiciated screws and replaced them with these MagicSliders chair "feet"
. Note: I only used the white nylon piece after slipping the brown/black plastic grommet off the nail. Unfortunately, these seem to come in packages of 8-40; I happened to have about 24 of them left over from a previous installation on our kitchen chairs. After installing the chair glides, I found that the drawer's existing center guide rail sufficiently keeps the drawer straight when opening/closing the drawer.
Surfing the web this morning, I found similar items at Lowes
, Ace Hardware
I recommend that, after removing the initial guides, you measure the clearance distance from the top of the side of the drawer to insure that you don’t get slides that are too thick. If you can’t find anything within that limit, you can probably chisel or drill out a bit of the wood crossmember that the drawer rests on where the glides will be installed to compensate.