It depends on where we'll be going and our experience or knowledge of the area. For Florida in the winter, for example, we make most our reservations for the following winter while we're there for the current winter in order to get the best site selections. In some cases such as the popular FL state parks, they fully book within seconds of the 11 month online reservation window opening for the winter months. We also book reservations for major holidays well ahead of time for the same reasons. Other times, we just "go with the flow", sometimes only calling a park an hour or two ahead of time to see if they have a spot for us for a few days. Most of the time that works fine, although we don't always get into our first choice park. Now, you did mention "resorts" though, so assuming you mean only those high end parks that cater to those of us with bigger checkbooks and high end RV's, they can be more selective in what they will allow in, no matter how far in advance you check with them. But there are also a fair number of parks with "resort" in their names that are really not worthy of the label, so "buyer beware" very much applies in park selection. Do your homework...
Dutch
2001 GBM Landau 34' Class A
F53 chassis, Triton V10, TST TPMS
Bigfoot Automatic Leveling System
2011 Toyota RAV4 4WD/Remco pump
ReadyBrute Elite tow bar/Blue Ox baseplate