I really don't see that much of an issue running 68 to 70 mph with a toy hauler travel trailer. It's not much more than the 65 mph speed rating of most trailer tires and some newer trailer tires are rated higher anyway. If you are worried about it, switch your tires out for LTs. I keep my tires aired up and check them every stop with an infrared thermometer. You could also go with a TPMS system for your trailer tires.
One thing to be aware of with a toy hauler travel trailer is the tongue weight is much more than advertised, even with toys in it. My toy hauler travel trailer has a GVWR of 9980 (dry weight 7020) with a 987 lb brochure tongue weight, but the actual tongue weight was 1660 when I weighed it coming back from camp with empty tanks. Toys in the back aren't going to take that much weight off of it. It's not a 1:1 ratio because the wheels are placed quite a bit further back than on a normal travel trailer. So, size your WD hitch accordingly if you stick with a travel trailer. Blue Ox and Torklift both make a 2000 lb capable hitch and I would recommend looking into those, considering your gross weight rating is north of mine. Just double check the weight rating of your receiver. You may need an upgrade.
