I cross the border with my van full of tools pretty regularly and I have not had a problem at all when asked I just tell them I am a carpenter and they are like "pasale guey"
If they suspect that intent is to sell the tools in Mexico then you may have a problem. If your Spanish is not good then sometimes they want to intimidate you to pay the import fee. If your Spanish is good then all you got to say that you are going to fix your property down there and tools will be coming back with you when you return to US, stay firm and brave and they will back down.
They will fight you on welders,chain saws and small outboar motors...recent experience.I find going Nogales way is always better when bringing things like this