I have used Geocell ProFlex RV with good success. I wet a small piece of paper towel with mineral spirits. You apply a small bead about 3-4 feet long then wet my finger from the paper towel with mineral spirits and lightly work it with my finger. Looks great when finished. You can get in different colors and clear. I sealed my belly band with the black stuff.
I have used lLexel but it seems to skim over instantly and does not work well. It's good for sealing in areas that won't be seen.
Dicor is also good stuff.
Only use 3M 5200 if you don't want to take something apart latter. Use 3m 4200 for that. Watch some utube videos.