Nope, nothing "exclusive" about the Trek.
But....
It is an organized and planned "event", not just a trail run with a bunch of buddies. We aim this primarily at folks from Outside for whom it is generally a once in a lifetime thing. Fees are paid, plans are made and slots are filled. We made the official announcement that the Trek was happening and that we were taking reservations here and a couple of other places on the 31st of July. Had our first commitment for a slot and fees in hand in about 4 hours after the applications were available to everyone IIRC. From Australia even.

We filled up pretty quick and actually had a couple of people on a "waiting list" status until just a few days ago.
Over the years we have held it to around 15 rigs or so. Total, including those of us "guiding" the event, the support trucks carrying parts, and fuel and gear, and any of the Alaska Cruiser Crew who joined in. One year we only had 3 rigs from outside! and we still had 12 total with all of the local and club guys who were there.
This year we had a very strong response and we decided to push upwards from out original limit of 15 rigs total. We will have between 21 and 23 rigs on the trail with us depending on whether or not a couple of The Alaska Cruiser Crew folks make it out to help or not. this is our Support truck and 5 Alaskan rigs guiding and helping out and the rest are visitors from Outside.
Really a bit larger than we would like if the truth were told. This is a LOT of rigs to wrangle for a week.
For an outing like this, the size of the group is a major concern. Impact to the trails, suitable places to set camp for the night and, often overlooked, rate of travel throughout the day...time to set and break camp, putting up "outhouse" facilities at each camp spot... Hauling more fuel along with us for more rigs, dealing with vehicle breakage (more rigs ALWAYS means more breakage.... All of this stuff is affected by group size.
We have always given Outsiders first chance at slots for the trek. This year we had to gently let a lot of the Alaska Cruiser Crew folks know that unless they were gonna be along as "help", there probably would not be room for them on this run. Sadly we have had to offer our apologizes to a couple of people from the 48 already too and tell them we are full
So.... nothing exclusive about the Trek. But it is a limited participation event simply because it has to be. At one point we had thoughts of up to 50 rigs on a Trek... yeah, that lasted for about 15 seconds before we all burst into laughter and groans of horror
Anyway, while I hate to say it.... we are not inviting anyone else to join us at this point.
Folks are always welcome to join myself, Kevin and others in the Cruiser Crew when we go out on our own. If you know what you are doing on the trail and you have a rig that can keep up on a particular run, you are always welcome. For that matter we are usually happy to bring lower experience guys and gals along too... New blood in the club is always a good thing.
This coming summer, prior to the Trek it is doubtful that we will have any outings that are not aimed at scouting for the Trek. In other words hard and fast, sleep under the rig, eat MREs and push onward. Runs after thr Trek is over will be largely dependent on how the trek goes. We may be out in the field recovering busted rigs for a week... it's happened before...
Mark...