The number of holes and their spacing is only one part of the information needed to get the right wheels. You also need to know the backspacing (sometimes called offset). I would NOT increase the size of the hole with a hole saw, the tight fit of the hole on the hub helps center the wheel correctly! Most trailer wheels use zero offset. Why don't you go to an RV dealer and get an exact match for the wheels you have now?
2015 Rockwood Ultra Lite 2604 WS. Rear LR, large street side slide with small wardrobe slide in BR.
2014 Ram 1500 Eco Diesel Laramie Quad Cab.