Heat problems when using 5 buck/switching converters in a double isolated enclosure?
Any enclosure that has power being dissipated inside of it will create a situation where the temperature will increase. The more that you cram into a smaller space the worse the problem can become. You should evaluate just how much heat each of the modules creates when in the proposed enclosure before you commit to a final design/build. It could be that you may even have to add a fan to force air through both enclosures to keep things cool. Remember that excess heat is the enemy of electronics. 

The flat yellow surface is just some tape wrapped around the transformer core. It is probably not the best gluing surface and the tape could easily come loose. I would suggest that after attaching your input and output wires that plopping each adapter into a good pool of hot melt glue may be a better mounting scheme. Just make sure that the hot melt glue adheres to the inside of your enclosure before committing to use it.

I have to ask why you think it is necessary to have five separate power adapters in one enclosure when the load on each one is so small. Maybe you could explain that with a schematic.