There may be a combination of 1/2 ton truck and 5th wheel trailer that remains within the truck's weight ratings, but both the truck and 5th wheel will be the exceptions, not the rule.
If you already have a 1/2 ton and don't want to upgrade, you will have to work within its numbers. Personally I would lean toward a travel trailer instead of a 5th wheel in that case. As already indicated, much more of the overall weight of a 5th wheel rests on the truck than the weight of a travel trailer.
If you don't already have the truck, I'd recommend selecting a truck that works for most RVs in the class you're looking for. This provides the opportunity for future upgrades.
Whatever you decide, I agree with others who already posted that you should study the weight ratings involved and understand them. It's great to get advice and people's personal experiences, but without knowing the parameters involved you can't evaluate the usefulness of responses. To be clear, all 1/2 ton pickups aren't created equally. Neither are 3/4 or 1 tos. Many, most?, 5th wheeler's don't fall within the weight ratings of many, most?, 3/4 ton trucks.
You will see people post here that they tow 70000 lbs with their Tacoma or Colarodo and you will see others say an F350 is overloaded with a feather pillow in the bed. The only way to determine your truck's capacity and ability to tow a given trailer is to run through the numbers. You may decide towing at or even above the maximum capacity of a vehicle is ok, others have. I won't comment on the merits of that decision, but I do suggest you make an informed decision.