I also had a spare tire carrier under the chassis aft of the axles. I have seen spares mounted on the ramp door which did not affect its use.
As others have pointed out, your 1/2t will be close to its maximum capacity. I would worry less about GCW and more about the rear axle weight and receiver capacity. Getting real world trailer tongue weight and truck rear axle weight with the toy hauler filled will give you an idea where you may need spend some money on upgrades (higher rated receiver or tires).