We used to have a TT like that. Not sure they do it that way sometimes. If you lock yourself out, you can always crawl in from under the bed... :)
Ours had 2 or 3 door hinges (like on an RV bathroom door) and had gaps and wasn't very well secured to the wall. I took them off, mounted a length of 1x2 against the forward wall and then installed a piano hinge. It's possible the lid may not lay flat when down and could use some tweaking. Had that problem in our current TT and had to do a little cutting of the luan and re-positioning of the framing on one side. Otherwise seems to me the mattress and bedding is going to stop insects from flying in except when you lift the lid and have a pass-through door open .
Better solution if you are handy is you could cut the OSB (or plywood?) and permanently affix the forward piece on top of the pass-through and install hinges or piano hinge between the two pieces so that when you lift the lid up only the under-bed storage is opened. May need to re-position the gas props and/or change their length and force rating. Some TTs are built this like our KZ.
Or for those with more advanced woodworking skills, you could install drawers or doors on the underbed storage "box" so you don't need to lift the lid.