I went a long time without a drybox... then I got a plastic NRS box. They don't make them anymore (for good reason, another story)... I liked it, but could live without it... it just wasn't that handy and had limited rigging options. Then a few years ago I made one from wood, exactly the way I wanted it. I put a sliding tractor seat mount on it and a high back seat, it sits on rails and is easy to strap in, but access is quick and easy - that thing I love. It's so easy to hop up, undo 2 latches and dig around to get rain coats, sweatshirts, etc. It keeps dry foods (on day trips; chips, bread, etc) from getting soggy in the cooler. For overnighters it becomes my kitchen box and food gets stored in buckets or boxes in drop bags. At any rate, I couldn't imagine not having a drybox, it's just too handy. I've actually gone to just bringing the dry box and a smallish soft cooler for beer and lunch cold storage on day trips. I leave the big cooler at home saving space and weight. I still spend way more days on the river day trip style than over night style and I really, really appreciate the handy access of a drybox.
BUT, I have two drop bags as well.... They are very nice to put spare pfd's, dry bags, any large items you want to get off the floor or out of the way. Drop bags with either hatches or flip up benches are also very nice... I just find that it adds another step or two to getting what I want out, and when your in a hury it makes a difference...
I tried lots of types of pseudo dry containers over the years but all had some minor quirks that dryboxes don't have. I think having both drop bag storage and a drybox is key, but that's just my opinion. They also just make almost perfect rowing seats, with a pad or with a seat added on...
I wasn't intending on trying to talk you into one, just to illustrate how handy they are, but I find myself thinking back to all my other storage experiments and realizing that the simple drybox was the one that finally hit the nail on the head. I wonder how much I spent trying to find cheaper or simpler options... way more than if I had just bought one 20 years ago! But it was a fun process along the way.