Start of by using a site like udemy (https://www.udemy.com), they are a platform for creating online courses and handle payments for you. They may have some users who are in your sector.

It sounds like finding 'customers' is your main issue. There is no panacea here, the approach you've taken so far is largely correct, here are some more ideas:

1. How about going direct to large construction companies (an industry you know) and offering them discounts for training their staff?

2. Reaching out to your own contacts to try and find more

3. Start a mailing list giving tips to these people and up-sell

4. The things you are already doing are good, blogging, social media etc. I would add creating meetup groups for engineers (and other target market).

5. Starting local is good idea, at least once you validate a customer acquisition model in the local area, you have something you can role out more widely.