Putting the ball under the camper will make it a lot easier to crunch your trailer into the camper on sharp turns.
A 3' extension isn't that bad. I use a 4' extension to tow my boat behind my 11' camper. I use a Torquelift superhitch. They are expensive but worth it. My boat weighs nearly 5,000 pounds.
For your small trailer you could get by with less. I used to use a 48" Reese hitch extension that fit into a 2.5" receiver. It towed the same boat just fine. I would think that Reese makes a 36" version.
If, however, you ever think you might tow a heavier trailer it might make sense to get the Superhitch now.