We’re both riding standard mountain bikes, a Commencal Super Normal and a Specialized Stumpjumper Comp. The bikes are both 26″ wheel, have front suspension and disk brakes. We don’t use a front rack and have instead put extra water bottles on the forks. The rear racks are secured using the QR skewer and the seat post, this even works with the trailer mount (after a small modification) and seems easily strong enough.
As we are camping we also have an Extrawheel Voyager trailer to carry the tent, sleeping bags, mats and cooking equipment.
Using standard mountain bikes means we can also mtb on them after the trip and they are still strong enough for touring.
Duct tape and zip ties. We brought plenty and it is true you can fix virtually anything with them, we already fixed the rack on the trailer, a bottle cage and secured several things from theft.
It’s useful to check every single thing you are going to bring to see if it is strong enough. If you can, strengthen it at home. Don’t assume because it is new it’ll last, the new things havent been tested and are the most likely to break.
Plastic water bottles have a death wish and are expensive, if you can use aluminium ones are work out a way to secure retail bottles to your bike.