I know a guy with a similar setup in an 85 4Runner and he used to tow his popup everywhere. It was slow going uphill but he did make it. I used to tow my 2 Seadoo's and had a cabover camper on top and would take it to Lake Isabella all the time from the desert side which was pretty big load and it was a 84 with a 22r, 5 speed, 33's and stock gearing. I did have to put it in 4wd low to keep it all cool but other than a slow go it never failed. I also used to tow my 18ft. fullsize camper trailer with my 86 4Runner with no issues at all, in fact it probably towed better than a 3.0 since it was a turbo. I would suggest a couple local test runs on it before you settled on doing it or not, but if your rig is in good mechanical shape you should not have much of an issue other than a slow uphill run.
