Sorry to be bringing bad news, but towing any vehicle and almost any trailer, with a Toyota motorhome is out of the question. This is an oft discussed topic on the several toyhome sites. Here's why:
1. Your 1988 has a GVW of about 5500 lbs and is at or above that already.
2. By 1989, when the v6 chassis came along, the builders finally started putting tags on them stating "This Vehicle is not designed for towing. DO NOT tow"
3. When towing with the 4 cylinder engine and A43D transmission, it is guaranteed that engine overheating and transmission failures will be in your future. When the 22RE engine overheats it often blows a head gasket.
4. In the past year at least two reports were heard of rear axle
failures, one was towing a 1500 lb baggage trailer, the other was acknowledged to be very overweight.
5. The braking system is "just enough" for the heavy coach body and your stuff. Adding a heavy trailer or vehicle will further overtax that system.
6. A Canadian couple, touring the U.S. with a V6 version, attempted to tow a Smart Car and got to do an entire engine rebuild as a part of the trip when it started burning valves.
7. General agreement is that small baggage trailers, up to about 500-750 lbs are OK, but towing a car is out of the question.
As Toyota sold the Cab & Chassis as an "incomplete vehicle" there were no tow limits published by Toyota. The coach builders finally introduced the "Do Not Tow" stickers after being leaned on by the NHTSA when they were being investigated about the rear axle
recall debacle on the 1979-1985 chassis.
Now, if you happen to have a 1988 Sunrader Adventure with a pop-up roof, it is light
enough to tow about 1200 lbs, but still not a vehicle.