TSP removes the wax, BKF removes any chalkiness from the fiberglass and hard to clean spots like black streaks. Use a 3m pad--preferably white and then rinse very well. I cleaned again with TSP, but I didn't use the powder--used a green liquid called TSP. (Same thing?)
Some people have just used their favorite cleaner of any kind and not bothered with the BFK but most who have used BFK find lots of other uses for it afterwards, it is a great mild abrasive cleaner.
Sun may just be uncomfortable to work in--I read someone applied in the sun and the drying went just fine. RMP dries very fast anyway. Just be sure to apply several thin coats to watch for runs. Good luck!