Been doing this for years. Make sure you check the trim level of the used van to make sure it fits the 4x8 sheet. I know in the past, there were some shorter van options. Stay away from those.
I've hauled anything from plywood and drywall, to lumber, flooring, concrete board, tools, furniture, landscape material, bags of dirt and stone, trash, and a lot of people. I know I have loaded more than the max capacity in the past, but never had any issues.
In addition, there usually is no issue with 10 or 12 foot material, set on the dashboard, and getting the gate closed. Careful closing it though! Don't shove a 2x through the windshield. I have done 16' before, but you need to Keep it out the back or through the front window.
As for keeping them in decent shape, always keep moving blankets around. Cover the floors and side panels and be careful loading items. While minivans are amazing, this isn't a truck bed. Bulk loose materials can also be problematic.
I've gone through 3 minivans in my time, and my dad, who showed me the awesomeness and is still doing fun remodeling projects, is on his 4th minivan. He wears those things out on miles before the interior goes.
Speaking of his adventures, he got the towing package on one of his vans and had routinely hauled a closed trailer to NY and FL moving materials and furniture for his projects.
Alas, I don't have a minivan right now, and have missed having one every day since. If I do get one, I will only get one with stow n go seating for the 2nd and 3rd row. This leaves the only options as Chrysler products, I believe after 2008. While Honda makes an outstanding vehicle, it's a deal breaker not having stow n go. If you plan on using the vehicle for people hauling more often than stuff moving, you don't "need" stow n go, but in my experience, taking out and storing the seats is a royal pain in the rear. Plus on multiple occasions, we have switched from all seats down to needing additional seat capacity while on the same trip. You aren't doing that without stow n go.
In all, the minivan will dominate most other vehicles for storage capacity. It has on numerous occasions hauled more than a pickup truck and any SUV. And you can close the gate and lock the entire vehicle and keep your materials out of the elements. And if I hear the damn argument about "just put the cap on the back of the truck" thing, guess what? You have to store that damn cap if you want to use the bed for bulk, and good luck getting people to sit in the back bed legally with it on. If you put a cap on a truck bed, you drive around in an SUV with no seats and less hauling volume.
Minivan for the win.
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