harding01screw

Hey guys. I have a 01 screw 4x4 with the 5.4 and the off road package. I noticed the other day when i was pulling a 10 maybe 12 ft steel flat bed trailer that even empty, my truck was sagging a little. I don't tow often or anything very heavy at all. Maybe will fill the bed with mulch or stone from time to time. My question is would i be ok with stiffening up the rear with a add a leaf kit from autozone or online some where? I dont wanna spend the money to totally replace the whole leaf pack right now as i dont tow much or plan on towing much. I know adding the leaf in the rear will raise the back end some but i plan on cranking my torsion bars to keep it level if needed. Thanks for any advice or opinions!