Mark,
Glad to have you back among the 'computer generation"
To answer your question about tongue weight/pin weight, a travel trailer has a tongue weight and it is usually maintained between 10-15% of total trailer weight. A fifth wheel, however, has a pin weight which is between 15-25% of total trailer weight. Recalculate your weights and you'll see that the 342 fifth wheel empty (shipping) weight is about 13000 lbs and the pin weight is about 3090 (23%). Toy haulers usually have fairly heavy tongue/pin weights when the garage is empty. That allows for the weight transfer when the garage is loaded and still maintain the tongue/pin weight within the percentage needed to maintain good handling.
The pin weight of the 342 at max GVW (18000 lbs) would calculate to be 2700 lbs (15% - low) and 4500 lbs (25% - high). Depending on the amount of load in the garage (behind the axles), the pin weight could change dramatically up or down. That's why you "plan for the heaviest" and weigh "as loaded for a trip" to be sure of where your weight really sits.
Nothing could spoil a "perfect setup" much worse than having a salesman talk you into using a 3/4 ton truck to tow the "dream RV' of your choice, only to load it for a trip and realize you need a one ton dually to handle the "real world" weights......