Moses,
The comments you have gotten re: dropping around from time-to-time when you know he's got some of these projects on the go are, I think, steps in the right direction. Only one trouble: If your Dad is an independent type, (and he sure as heck sounds like it) he will be the sort who likes to think about something for a while, then go and see if what he has thought about will work. If so, then he goes on, alone, knowing this is getting the job done, just as it always has.
If this seems to be the way things are, the only thing I can suggest is getting in on the planning stage. Make yourself aware of his projects, be prepared to sit and chew over the possible ways of tackling a job, then be there when the urge strikes him. It might be impossible, for a while, as many 'independents' do so because they do not wish to share their failures with others. Having someone around while the project is in progress opens them to someone else's pace and possible criticism. You can tell this is going on when you hear him say, "No. I think I'll get around to that next weekend." Then, when you show up 'next weekend', the work is done and he says, "I just had a minute so I thought I'd see if it would come off, (or go on, or work or whatever.)
On one hand, I miss my 'independent father', who passed away 9 years ago, this month. On the other hand, when I get up to my neck in a project which probably would have gone easier with help, (which is available, but I didn't ask for), I can't help but think, "He lives in me."
He has been doing this for almost all of his life. You can offer, but you can't make him take you up on it. You might cramp his style.
Les