Beth, with an inconsistent process, I would think you would want to go with a stock item in inventory supported by a BOM. What would change by season is your stocking level. In the slow season you want to set your minimum stock to 0 and your minimum order quantity to 1. That way you only build the kits you need based upon current demand.
In busy season, you would raise both the minimum stock and the re-order quantity so you maintained adequate stock levels to support demand.
Either way, you would use a report to identify the quantity to assemble and process a BOM transaction to back flush the assembly process.