Mid summer anywhere around the Great Lakes can be hot and humid, May or Sept would be the most comfortable.
Note: I've been in Toronto and the Canadian side of the Falls in mid July, temp was 107f and humidity was 95%, thunder storms every night.
RV parks along the East Coast start shutting down in late Sept, too cold to keep the water flowing. Any area you plan on staying check for RV park web sites for seasonal closures.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.