I'd bet you weren't hassled because of too many visas but more like too many free visa exempt stamps and no actual visas. As Tod suggested, get a SETV and border bounce or a METV and you should be fine because those are actual visas which you are paying for. And just for clarification, it's not customs who hassle you, it's immigration, as they are the government body who allow or deny entry, whereas customs are only concerned with what you bring with you.
Have a look in your passport, your next report will be stamped on the report receipt stapled inside your passport, which may be from your last 90 day report or if the IO gave you a new receipt when you did your extension, it will have the new date.
3. If you are seriously considering applying for a 90 day non O retirement visa then you should do that before you come. A key requirement of that visa 1 year extension is to have 800k thb in a thai bank account in your name for 2 months prior to the extension application, and given the changes/clamp down on opening bank accounts, it will be nigh on impossible to open an account on any type of tourist visa, including the visa exempt stamp.
Bin the report in your passport and ignore any email reminder of your next 90 days from your OLD report date and start your NEW 90 days with your new entry date as day 1.
Remember, you are reporting 90 consequitive days IN Thailand, so if you leave and return, the 90 day clock re-starts.
As you're travelling in a camper van the only way to do the 90 day report at your location, is to book into a hotel for 1 night and get a copy of the TM30 they should file. Other than that, just report late when you get back home and take the 2000 baht fine.