Since you already have the equipment, your cost to redo the zolatone will be lower than for someone who has to rent or buy the equipment. But will redoing the zolatone raise the final sale price by enough to justify the expense? Maybe not. Not everyone attaches value to new zolatone, depending on what they have in mind for the trailer.
You could do things another way: Sell the trailer as-is, but then separately offer to redo the zolatone for the new owner for just the cost of the materials before he takes delivery.
That's advantageous to the new owner: If he wants it done, he can get it cheaper from you than doing it himself, but if he doesn't want it done it doesn't cost him any extra.
That's advantageous to you as well: If he wants it done, you know you'll get paid for the new zolatone, but if he doesn't want it done, you're not out the cost of materials.
Win/win is always a good plan.
Engineering: Finding complex solutions to simple problems you didn't even know you had.