Hi JB,
Yeah its safe to keep gas bottle in the engine bay. The early Bay Dormobiles had the gas bottles in a wooden tray type thing secured by straps on the left hand side as you look into the engine bay.( there should be an isołation cock just in front of the spare wheel to turn off at bed time).
Providing everything is tip top maintenance wise,The engine bay is a lot cooler than some think.after all, cooling air is being drawn in at a fair rare of notts by the fan. My only concern would be if the engine and associared bits are not maintained such as seals and fuel lines, in which case thd engine bay will get hotter than it should and presents issues like over heating, fire etc.
In short mate,if VW and Dormobile were happy to put the bottles in the engine bay & if everything is in good order then thats good enough for me. Personally, I’d rather the gas bottle out there where there is ventilation than in the bus where the kids sleep and its enclosed.
Just my opinion, hope it helps! 🙂