Try using the pip caching in the tox config.

.travis.yml

@@ -9,11 +9,6 @@ cache:
     - ~/.cache/pip
 env:
   global:
-    # These two environment variables could be set by Travis itself, or Travis
-    # could configure itself in /etc/, ~/, or inside of the virtual
-    # environments. In any case if these two values get configured then end
-    # users only need to enable the pip cache and manually run pip wheel before
-    # running pip install.
     - PIP_WHEEL_DIR=$HOME/.cache/pip/wheels
     - PIP_FIND_LINKS=file://$HOME/.cache/pip/wheels
   matrix:
@@ -51,7 +46,9 @@ env:
     - TOXENV=pypy-dj17
     - TOXENV=pypy-dj18
     - TOXENV=pypy-dj19
-install: pip install tox
+install:
+  - pip wheel -r tests/requirements.txt
+  - pip install tox
 script: tox
 branches:
   except:

tests/requirements.txt

@@ -0,0 +1,8 @@
+coverage
+django-discover-runner
+mock
+dj-database-url
+dj-email-url
+dj-search-url
+django-cache-url>=0.6.0
+six

tox.ini

@@ -22,14 +22,7 @@ setenv =
     DJANGO_SETTINGS_MODULE = tests.settings.main
     DJANGO_CONFIGURATION = Test
 deps =
-    coverage
-    django-discover-runner
-    mock
-    dj-database-url
-    dj-email-url
-    dj-search-url
-    django-cache-url>=0.6.0
-    six
+    -rtests/requirements.txt
     dj14: https://github.com/django/django/archive/stable/1.4.x.zip#egg=django
     dj15: https://github.com/django/django/archive/stable/1.5.x.zip#egg=django
     dj16: https://github.com/django/django/archive/stable/1.6.x.zip#egg=django