The vertical post connection is much stronger than you might think by looking at the photo, especially without any scale for visual reference. But I still like the sound of your triangular "2-pin" support suggestion.
The aluminum "straps" are heavy grade and the stock is 1.75 inch square - hefty stuff. The forces on this connection (especially the horizontal forces) are quite small. The attachment really only needs to be strong enough to resist the whole setup from rolling away. Even on a modest incline, such rolling forces are quite small.
The connection itself, while over-designed to support the bows of a boat, is mainly designed to be easily removable during the process of loading/unloading a boat from a trailer.
It is strong enough now so that it is not possible for one man to break/bend that joint by pushing or pulling on the boat - even with the vertical post planted on the ground (I`ve tried that).
The back wheels/axle take at least %90-95 of the overall load. The forward hull support has just enough flex to prevent shock loads to that connection in all planes. The forward support is designed so that when the boat is pushed forward, (while the Hometrax are held stationary) the boat SLIDES over the forward support - with just enough resistance to be comfortable - rather than putting unneccessary forward force on that connection. Keep in mind, when a boat has to be slid forward on the Hometrax, the post is actually planted "on the ground" gaining some extra support and holding power, thereby reducing the stresses on those aluminum straps. This is partly because the whole boat is repositioned very easily by either leaning your backside (straddled) or torso up against the T-handle and pushing or pulling the boat depending on what you`re trying to do.
Also keep in mind, the post is secured with a 5/16th pin and two slabs ("straps") of heavy grade aluminum secured by two 5/16th stainless steel bolts. The breaking/bending forces of that connection range from 2 to 3 thousand pounds vertically (maybe more) and a few hundred pounds (at least) horizontally given the lever length of 18 inches to the bottom of the vertical support.
In the method of a good scientific approach, the main things that I can think of that could over-stress that joint would be;
(1) Someone jumping around on the tramp while the Hometrax is on an incline (2) Gaining speed with the whole contraption (loaded) and dropping it; suddenly forcing the vertical support to act as a brake. (ie. spiking it into the ground at speed) (3) The boat left unattended on the Hometrax to bounce around in a storm without first: sinking the vertical post into the sand (like a spike) far enough so the bows touch ground; OR removing the forward support altogether; Or (most important) securing the entire boat and Hometrax appropriately for the given weather conditions...I have already learned "the hard way" that the H16 likes to fly - trailer, Hometrax, with or without you! I think it is best to secure it all...very well!
Incidently, I will be cutting that post from its existing 18 inches down to about 12 inches. The extra height is not necessary and will make it even easier to store in my 20 inch wide catbox - I prefer to leave the vertical post attached to the horizontal (tubular) hull support during storage.
P.S. Still, I must admit I do like your idea. But, not so much for strength (although that is an added benefit). With a triangular 2-pin support permanently secured to the vertical post, I could put one pin in place with the support folded under - like a folding table leg. Then by lifting (straightening) the "leg" into place - simply by lifting the T-handle - the hulls would raise and the support would slowly swing down into position by itself. Then I could put the second pin into place. I think this would be better than holding the whole assembly up with one hand and pinning it into place with the other hand...I like it!