Take the time to take the car apart to install the weights properly and evenly. Going through the doors is asking for an unbalanced car. The weights should be added centered over each of the trucks to prevent the floor from sagging and to concentrate the mass onto the wheels/flanges. On eBay, there are several sellers offering stick-on 1/2 ounce iron wheel weights (or lead if you prefer). These are the ones I bought:
https://www.ebay.com/itm/1-2-O...Priority!90710!US!-1