I installed 12' of 1 1/4" T track on P&S cap rails.
1. carefully mark track location "first bolt hole" each side
2. with a helper holding the track outboard
and with first hole in position, drill and fasten first fastener, snug but not tight.
3. move track inboard until second hole is in position, drill and fasten as in step 1
4. repeat until all holes have been drilled and fastened, track will easily bend to fit the curve of the cap rail. You can chose to either caulk the holes as you go or wait, remove the track, then bed