I need a CRM solution for my case

Marketing Director for a very small company. We sell services, products, and equipment to the asphalt industry.

I need a CRM solution to keep track of the following information:

1) I need it to track who the site manager is for each location in a company, but it needs to allow the same contact to be associated with multiple locations.

2) I need it to be able to store equipment data for each location. (condition from last visit, how many they have, serial numbers and model numbers).

3) Wish list item, but I have field techs who have to access this stuff remotely, and sometimes their service is terrible. An offline solution would be nice.

So far we have tried working with Hubspot and Agile, but neither could do what we wanted without having to perform multiple workarounds and our techs don't want to sit around for a week-long training. I am open to developing our own CRM and if there is an open-source option that allows this customizability I am on board, but I would prefer not to have to spend the time developing it.