I would just like to add, as a mother of 2 SPD children one avoider one seeking, our oldest is 4 and 1/2 and was only just now potty trained 100% cept when sleeping then he goes in "night pants" AKA pull ups..

I would sugest, no pull ups, but if you dont want a constant mess, to use cloth diapers, you can make a handfull for everyday use pretty cheaply, and use pull ups only at night... also
with out child we made a BIG deal when we had to go potty loudly saying if we are peeing or pooping, and rushing to the bathroom and letting him watch. I also pumped him FULL of juice for days and days, when we were home at this time i used the the bare bottom, and we tryed stickers but,they didnt work to well what was the best for us was everytime he sat on the potty was a HUGE clapping hooting fest, and LOTS of talking about it even 10 minutes later we were saying , Man that was SO awsome when you peed high five again...
he also had his own small potty so we could Sit together... hes a bit OCD so we actualy Just recently got rid of his small potty, he didnt want to use our big potty even tho out in public he had no problem using the bathrooms.... we also took him into EVERY bathroom of where ever we went.. so lots of extra exposure...

good luck, its pretty hard all together, and our youngest who is almost 3 and has very little language (is now just getting some) and few ASL Signs, she seems like shes a LONG way off from the potty.

But as i cried to my hubby yeaterday, we were camping and We both got stressed at our 1st trip with the kids (we dont do much with 2 kids with SPD, even shopping trips are nightmares on a daily base) I said , "I just want to do something NORMAL, and have a experiance with the kids, thats NORMAL!!!!" and sometime you get normal, but 99.9% of the time you just have to clean up pee for the 1000th time in a day in the hopes the lightbulb clicks on and the message dosnt get re-routed.