Here is a view of the fuselage bottom, prior to the UND glassing. My decision to place the NAV antenna where you see it was based solely on the fact the RST manual stated the optimum angle for it was 10-30 degrees. If you place the antenna per plans, there is no way you can fit it with less than 45 degrees. THERE!
For the coax routing, I chose to merely Dremel a channel just wide enough for the coax, stuff it down. Then take some left over bulkhead foam, taper it a little on one edge. Put some micro in the channel. Jam the bulkhead foam into it. After it cures in place, sand it level. Worked pretty good, if I do say so myself. Others have "pour foamed" the coax in place, but I'm trying to stay as far away from that stuff after reading how it sometimes wants to expand/contract after cure.