Is there any reason to coat or prime the inside areas of the plane. I 
am ready to start installing the lines?

I plan to coat the wheel wells with tank sealer, but the rest seams 
like a waste of added weight.

Kevin,

 

It has been useful to coat the base of the tunnel, parts of the belly and an area around the hydraulic pumps because leaks from the hydraulic system are very difficult to clean from untreated glass/carbon.  You will have a leak.