I'm trying to visualize some of this, and I know you have a futon, but have you tried a plastic zippered under bed storage system? I have at least one in each bedroom, and it's where the extra blankets are stored. In summer I pull off all but a thin thermal blanket and put the washed and folded regular blankets into the bag. If could could fit something like this under (or behind) the futon, this might give you room for something else in that trunk. For example, I got tired of all of the bins of dog food sitting in view next to the door, so I pulled out one of my antique trunks large enough to fit both and store them inside. Now that trunk looks interesting next to the back door, but it actually is doing an important job.

I'm sure WalMart and K-Mart and Target and Sears and all have these kinds of storage bags.