I used machine screws on mine with the stock black chassis (these are recent kits so I don't know if there's any new change) I tap the holes with a "gun tap" that is about half way between a starter tap and a bottoming tap. You must be patient while tapping. Take care that the tap enters straight and that you remove it straignt up so as not to damage the top threads. I use a thumb and one finger to turn the tap handle by it's collet. Do not use the t handles or tap too quickly as you will possibly overpower the tap when it gets to the bottom of the hole. This will strip out the threads and you will have to get a new chassis and start over. On softer plastic like the shock mounts on the suspension arms I use tapping screws. If you have an old chassis plate, a bit of practice wouldn't hurt.

At the present time I use 14 titanium machine screws on the main chassis. 4 each for the 2 diff covers, 4 more for the gear cover and 2 for the front bearing cover. For the steering arm mounts I ream out the screw holes with a 3mm reamer and use a long machine screw with a lock nut inserted into the lock nut socket visible from the bottom of the chassis. This way you can be pretty precise about bolting down the steering gear without having to worry about stripping the plastic chassis hole. My M3 x 10 machine screws come from Yokomo and any titanium tapping screws used come from the Yeah Racing TT02 titanium screw kit which is presently out of stock on this date. All are hex tool screws

My thoughts are to use machine screws in those parts that are removed for maintenance like the diff covers and the tapping screws elsewhere to avoid having to tap about 2 dozen holes. Sorry that I don't post here more often but I've been racing since 1973. Back then it was 1/8 scale nitro cars in the Roar 73 series.