Problem--excessive weight
Solution--remove excessive weight
Yeah...you have probably been bouncing off the bumpstops for some time. New shocks still may not solve your problem...for long.
I have had 3 adults in the rear of my car and it doesnt hit the bumpstops (if I am careful) but you cant drive it like you stole it with that much weight back there. HOW much does that beeyotch weigh...?
Not sure what gen you have (think i saw pics and it looked like a 4th) so you will NEED full struts all the way around. Tokico is prolly your best choice...so good researching. Older gen 4's allegedly had rear strut mount problems so if you have a 97 or so the guy might be telling you the truth. You can buy them from the many online parts stores...1sttoyotaparts.com; I think. With a haynes you can do it yourself and save some bank.
But really...to avoid this in the future remove that heavy ass box.
BULLMKT