Coatings are a big no no IMO if you're working mobile. Application requires too much to safely/properly do outdoors. As for waxes and sealants I usually reach for poorboys world stuff. I really like their EX-P sealant and have no issues with it in the sun even on black cars. Their nattys wax is just as easy. I also really like polish w/ sealant for a quick one step but have migrated more towards using HD speed for my one steps the past few months. I'm sure there are other options out there but I haven't tried too much else. Most products are simply just not sun friendly and will just give you fits from the second they touch the paint
Working out in direct sun has its challenges and you have to be conscious about what you're doing. The biggest challenge is keeping the car wet while washing it, or making sure a product that needs to dwell for some time doesn't dry up. You may find yourself using more product than you would need in the shade, simply to keep the surface wet. When stuff dries on the surface it wreaks havoc on the whole process. If you're doing a traditional 2 bucket wash, get in the habit of washing a panel, rinsing, washing the next panel, rinse both panels, wash the next, rinse all 3, and repeat for every panel until you're rinsing the entire car all at once. This will keep everything wet and prevent water spots until you can go back over with a drying towel. Your other best friend will be rinse less washes. They work great in direct sun. Wash a panel, dry it immediately, move to the next. Water doesn't have a chance to dry up.