For orbital polishing it pays to invest in a quality polisher/sander.
The key is a "wide adjustable rpm's range" and power.
Mine has a no step range of 750 to 3500 rpm
I invested in a professional Black & Decker unit some 10 years ago .
At the time it was a lot of money. Now that most of this stuff is made in
China
it should be considerably less.
You must avoid heat built up at all cost. Luke warm to the touch is OK.
If too much heat is generated the gel coat will bubble
Udo

There seems to be a broad range of prices (from ~$30 for a Ryobi 10"
orbital polisher at Home Depot, to $190 for a DeWalt DW849 polisher,
mail order), so this is an investment I want to get right the first
time.