Done several long trips in M3 since 2018. Planning a 3+ week trip now for May!
Use A Better Route Planner, and Tesla route planner, to layout trip. Figure what we want to see and do along the way, then general areas where stopping for the night makes sense. If hotel in the area has EV charger (PlugShare helps here but have found it’s not always accurate) and is not a lot more expensive than similar hotels in the area, will probably stay there and charge overnight. If not, will just use nearest Supercharger and charge before bed (preferred) or have breakfast or take walk while charging in the morning. To see driving route and what’s along the way to sightsee/visit use maps on ABRP, PlugShare and Google Maps. After you pick a possible area to stop for the evening, check hotel prices 30-60 miles before and after there because hotel prices can vary a lot.
Usually charge up a bit more than what ABRP suggests to have extra juice to take impromptu short side detours off main highway to visit things along the way.
It is free to join hotel* frequent guest programs, you get discounted rates and decide if you want to book lowest non refundable rate or a slightly more refundable rate based on how flexible or not you can be. I found some Holiday Inn locations with T destination chargers really charge premium, so cheaper to stay at a Hilton and then visit a Supercharger. Hotel websites usually indicate if they have EV chargers, but not always. Have not done a trip where we haven’t reserved a room at least 3 weeks ahead of time.
* Hilton, Marriott, Choice, Best Western, Holiday Inn
In some more rural areas, you can charge at RV parks if needed. Stayed at a small house via VBRO and was able to charge in the garage ( brought extension cord). Cord was handy when staying at a motel, parked in front of room, and was surprised to see wall outlet near the door so plugged in!
Lastly, can call hotels and ask if they have EV chargers and confirm cost or no cost. A Best Western in AZ charged us even though their website and front desk made no mention of a fee. The Doubletree in Biloxi places orange traffic cones in their EV parking spots (nice touch to prevent ICEing) so you just move them aside when staying there and move them back when you leave!
hope this helps!