With a travel trailer, the tongue weight should be somewhere between 10% and 15% of it's total loaded weight. And, yes, you should shift weight around inside your trailer to achieve that. If you go to a fifth wheel trailer, approximately 25% of the trailers weight should sit in the bed of your truck. Again, you may have to shift weight to achieve that.
This brings up another point. Somewhere on your truck is a sticker that not only gives the truck's Gross Vehicle Weight Rating, it should also give both Gross Axle Weight Ratings (GAWR) - in other words, how much weight each axle can safely carry. With either a travel trailer or fifth wheel, you need to make sure you don't exceed the rear axle's GAWR.
In addition to weight, many towing guides also show the maximum Frontal Area (in sq ft) that the vehicle can pull. Remember that dragging a trailer down the highway is akin to pulling an open parachute behind your truck.
Finally, just because a vehicle is rated to pull a trailer of X pounds, that doesn't mean it's a good idea to pull that much all the time. I've seen a rule of thumb that you should have a trailer that weighs no more than 80% of your maximum towing weight. Try pulling 100% all the time and you will certainly shorten the life of many of the components on your truck.
Let me just add that in addition to using RV forums like this one as an information source, you should also look for a Toyota Owner's Forum and use that as a cross check. You may well find more Toyota owners who tow there than you do here.
