Here's my opinion as a former Fed Ex cargo can loader:
1) Find yourself a really good box. Since you are sending a 4 piece kit, the items you are sending is considered oversize, so I doubt you will find a box big enough to fit all in one box. If you want to play it save, use a box for each piece. I've seen car parts without boxes poorly packaged, usually they are the last item to be loaded onto the cargo can. These are items that are stuffed in, thrown over the top, and/or kicked in to fit inside the tight can.
2) Use big bubble wrap, not the small kind for gift boxes. But wrap that is at least 1/2 inch big. For the abuse it could get, you want to cover/wrap it at least twice and enough that it will survive a hard toss onto the ground. I recommend wrap the product to insure it will handle the abuse.
3) I do not recommend peanuts, if you do not use enough inside the box, the penauts will move around, and if you stand the box up, all the peanuts from the top will fall to the bottom. Once it thrown, there will be no padding from the missing peanuts, so you'll get a dent, or worst, a broken part.
4) Tape, tape, tape the box properly. I've seen poor tape jobs, usually with poor boxes. Once your box is open, your items will move around, if you use peanuts, it will fall out and no more padding. Worst of all, you might get someone dishonest it will be stolen.
5) Don't underestimate using insurance and marking your box with 'Handle with care' or 'fragile' stickers. Insurance, if it's lost or broken, you get your money back. With stickers, there is no guarantee that it will be handled with care but if your box came to someone like me who takes pride with their work, I would be cognizant and wouldn't throw the piece around.
6) Make sure you fill out your shipping label correctly! Do not skip or miss an item. Enter receivers telephone number, and enter the last four digit zip code if you know it. I've seen shipments delayed and people pissed off! Well, you didn't fill out your form correctly.
Taking these small steps will insure that your package will be sent safely and securly. I've seen too many shipments broken or destroyed and I can say with confidence that 99%, it's because of poor packing. Also, you will hear the story, "Well, Fed Ex, UPS, DHL, ect, ect, ruined my package" Let's see a picture and I bet one of the above steps will match.
i work for UPS, and honestly if its securely boxed up you should be fine. Usually the person who loads or unloads don't give a cra*p for customer packages. BUT for light packages such as kits, you should be fine. ONLY packages that are VERY heavy, they just toss the package to the ground like it's a POS.