Shipping big items: help?

I have never shipped anything big before and am about to do so.  I have a spoiler and a rear lip kit that I need to send out.  I dont have a box for these two items.  My question is: 

1) can I bubble wrap each of these and slap on an address to ship??? 

2) where do I go to drop these items off?  I want to say post office but do they have a big enough scale to weigh these items?  I dont want to walk into a post office and look like a fool carrying these things around lol!  Or should I go to a ups or fed ex office to ship these?  Do they have a scale to weigh these??

Sorry, rookie here.

The lip kit might break in 2 if you just bubble wrap it. I say look for a box store around your area and see if they have a big enough box to fit your items.
If they don't have one then you probably need to be creative in making your own box for it. 

After making a box get a FRAGILE tape and slap it around the box and when you take it to a UPS or fedex tell them to put a fragile item on the label
UPS, fedex or DHL might be cheaper than USPS for big items

when my bumper got shipped from over seas they wrapped it but they really WRAPPED IT layers on layers of bubble wrap followed by news paper then some type of brown paper and it was in this huge bag type packaging not really a box but more like a sack type bag long enough for the bumper and the label was on it lol...not too sure how i felt about that but the bumper was fine so i guess its fine

You might want to try a freight carrier. I have a buddy who owns a freight company, I can give you his info if you're interested. The rates are usually better than UPS, etc. FedEx does have a "Freight" division as well, so maybe contact them too.  When I got my VS sides and rear lips for the Q they were in a big ass box delivered by a random freight company.

Thanks, guys!!!  I guess I'll have to alter boxes to fit the rear lip.  The wing is more manageable but heck, its like 65" long so Ill have to find a box for that.  The lip is a big "C" shaped so..