This was a great way to see the island and save money. Personally, it was better than staying at a hotel. If you are on Kauai for a long trip, consider splitting the trip half in these popup tent trucks, half in a hotel. If you are going to multiple islands, do th camping part of your trip with these guys. They have everything you need in the trucks, and they are very responsive to your needs.
Initially we were worried that it would be difficult to find places to stay. While you can't camp right on the beach, the beach parks are great. Get permits at the County or State Parks. There is very little enforcement, so if the park you want is booked full, buy a permit for a different park (to support the parks), but go to the one you want.
We stayed at Anini Beach Park the first night, which was great. The second night we camped in Koke'e State Park on the edge of a cliff looking over Waimea Canyon.
We spent days on the beach using all the gear. Careful, don't get the truck stuck on the beach! It could easily happen, even with 4x4.