I've seen problems with Eterna Bond tape so I do like ajriding said above and use lap sealant around my hatches and vents. I mask a discreet square area around the hatch and vents and work the lap sealant back and forth with a throw away brush. This insures working it into the surface and then pull the masking for a nice straight line around each one.
My factory hatch hinge was so close to the roof fiberglass I couldn't get a proper seal so the hinge leaked. After building an all new hatch in stainless with the hinge higher off the roof all is well.
Some openings on a fiberglass camper have wood around the rough openings, not many, so I did not know about yours. Mine did not.
BTW. my roof is warped upward where the wet bath is but it's minimal. The factory did that with the wet bath stall put in before the two clamshell halfs were together. It no biggy.
Bigfootford is correct about where the water goes you will see stains on the wood. Sometimes very slight or mostly down in the bottom of those bed side cabs.
