A lot depends on the size (width) of your slideout and the mechanisim that moves it in and out. The larger the slide, the heavier it is and the more beefy the motor and gearbox.
We have a 77 inch slideout and I loaded the pantry and put 2 cases of wine, 2 cases of water, and 2 cases of beer in the dinnette slide and it would not close. The clutch in the gearbox would just slip.
Moved stuff around and it closed just fine, for example.
If you are going to mod the slideout and you plan on a heavy load, you may want to call Lippert (assuming they made your frame) and ask about beefing up the slideout motor and gearbox.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW