Probably will drill the NMO holes when I pay the truck off and the mount or cable or antenna start giving me issues. I agree the best way to mount is the roof but dealing with parking garages in my previous occupation a roof mount was not gonna work real well especially for a 49" CB whip, so I just kept the mounts where they are since I already had them there. Besides dropping the headliner was a pain for some other things don't want to do it again unless I have to.
I am considering a Laird BB4503 15" 5/8 wave or a Laird TRAB4503 Phantom for my fender mount. Both are advertised as 3db and where I live and drive is a mix of suburban and some small hills so I think the 3bd would be an ok choice. Not too concerned about looks or stealth as I already have a CB antenna on the other fender. Either will probably work good with the TK-8180 I have coming.
How well does the Larsen pancake work? I am assuming it is not tune-able. I can't find anything indicating it is. I am considering it for a few mobile (car wash, parking garage, etc friendly) installs for friends and family.