Assuming 200lbs of force to drag it up the slope, 23.5 deg from horizontal.

Angle = asin(drag force / weight)

If you want to only pull with 100 lb of force then 11.5 deg slope.

This is of course assuming no friction as using a set of beach wheels on a prepared surface will be close enough to zero friction for this purpose.

If you really want to get it dead on, determine your coeeficient of friction and use this formula:

Pull Force = Weight[Fcoeff * cos(angle) + sin(angle)]

But again, for practical purposes you can assume no friction. If you want to be sure multiply your desired pull force by 1.1 to "build in" a safety factor.