Single axle trailer for a 21' Excel SX?

[96 Wellcraft]

I looked at used boats for about 4 months this year before deciding to buy a 1996 Wellcraft Excel 21SX. Prior to choosing this boat I looked at several without trailers. When checking on new trailers, all of the dealers told me I would need a single axle for anything under 19' and a tandem axle for any over 19'. My 21' boat listed at 2900 lbs dry is on a single axle trailer. The trailer is a 96 Ez Loader with surge brakes and torsion axle.

Am I ok with this setup? I have towed it behind my 02 Silverado Duramax Crewcab 4x4 about 200 miles total (3 different short trips). It seems to tow well , but I want to eventually tow it to the coast of NC about 7 hours and 450 miles.