open to any forum member with 100 (or whatever) *real* and useful posts as of April 10 (or whatever date).
That will be a problem. Firstly, to define (you will have arguments out the wazoo) and secondly, to implement (how much work would be involved?)
It's an arbitrary metric wholly decided by Dave. But it's like porn... you know it when you see it. There's nothing wrong with limiting in any way he sees fit.
Having said that, and on second thought, I personally think it should be forum members who were registered before the video date and with X posts. Otherwise, when word gets out (and it will) that all you need to do to possibly win a $15,000 scope is register on a site, there will be TONS of registrations from people who have exactly zero interest in electronics who are dying to win the scope so they can toss it up on eBay.
I would the criteria Dave cares about are contributors or legit users, and I would bet the manufacturer would just like it to go to an electronics guy - whether a noob or an old hat or a hobbyist or a pro - as long as it's someone who is interested in electronics.
Side note : I listed some free parts on Craigslist (essentially the free want-ads for those not familiar). Within minutes, I had dozens of replies... "I will take it!". Upon trying to be fair and reply to the first guy, he said "What is it that you are giving away again? Can you send me a list?". There are tons of people that troll Craigslist for free stuff then try to sell it right back on CL or eBay or whatever. Screw those folks. And a $15k scope? That would be the win of a lifetime. If word got out, the number of non-electronics people registering for the scope would exceed by far the total number of existing users, making it likely one of them wins and not a legit user.
Dave can do a video announcing the giveaway and saying it's open for EXISTING forum users, then mention that there have been multiple giveaways in the past, so people should sign up for the forum and participate so they are in the running for the next one.
Anyone who isn't really interested in the content won't likely register and be an active user for the chance to possibly enter a future drawing - too much work for a selfish asshole without guaranteed reward. But it will encourage legit users to sign up and participate.