When I first bought my MH, I paid and RV shop to seal it. It was a complete waste of money. I would have done a better job cleaning up before putting on fresh lap sealant and they didn't even touch the windows.
I am a fan of Eternabond. It unrolls like a tape, but it adheres like crazy and is a great solution for all your top seams. Put it on under the metal trim and it will be water tight for 10+ years, with no need to re-apply between. You do need to have a metal roller to really get it to stick, but it's awesome stuff.
Jose